These last devices are for location at least partially within a patient's body for a period of at least the order of a day and comprise means operable to generate an electric field acting, in use of the device, to inhibit bacterial attachment and colonisation on and adjacent to the device/body interface. In one device form the generating means comprise an electrode for or in connection with an electrical circuit, the electrode being supported by the device and the circuit being operable to generate the appropriate field by way of the electrode.